Yichud is the prohibition for a man to seclude with a woman that he is forbidden to lest he be intimate with her. This applies to secluding with a non-Jew of the opposite gender as well as a single woman.
- It is forbidden from the Torah for a man to seclude himself with a woman to whom he is forbidden. It is Rabbinically forbidden for a man to seclude himself with any woman, even a single woman or non-Jewish woman. It doesn't matter if the woman is Jewish or non-Jewish.
- It is rabbinically forbidden for a man to seclude with two women.
Multiple Men and Women
- It is permitted for many men and women to be secluded together. What constitutes many men and many women? Some poskim write that only if there's 3 men and 3 women, some say 2 men and 3 women, and some say 2 men and 2 women constitute many men and many women. The poskim are generally strict to consider it 3 men and 3 women.
- If the men are involved with inappropriate activities (פרוצים), then it is forbidden even if there are multiple men and women there.
One man with multiple women
- According to Ashkenazim, some permit one man to seclude with 3 or more women unless in profession he deals with women. Others forbid.
- Those who are lenient about this allow one man with three women even at night in extenuating circumstances.
- According to Sephardim, one man may not be secluded with multiple women.
One woman with multiple men
- According to Ashkenazim, a woman may be secluded with two men, as long as the men are not prutzim. According to Sephardim, this is forbidden.
- It is permitted for a man to seclude himself with his mother, daughter, granddaughter, or wife even when she in her state of Niddah. It is permitted to have yichud with a granddaughter, whether she is a daughter's daughter or a son's daughter.
- It is permissible for a man to seclude himself with his sister, however, it shouldn't be done frequently. A brother and sister still living in their parents home may be left alone together for only a few days and not for an extended period of time.
- Yichud with two sisters is forbidden. Some say that yichud with a mother and her daughter or grandmother and her granddaughter is permitted.
Husband in the City
- If a woman's husband is in the city, it's permissible to seclude with her unless one has a close relationship with her (Libo Gas Ba) such as if one grew up with her or is a relative.
- What is considered a close relationship such that there is no leniency of having one's husband in the city? Some say that even a professional acquaintance is considered a close relationship, while others limit it to a step-sibling or a relative.
- Some poskim hold that this only applies if the husband can come at any moment but not if a person knows that their husband isn't coming home until a certain time since he's at work or is involved with a specific task. Others are lenient.
- Some poskim hold that this leniency does not apply if she's not at her own home. Others are lenient in extenuating circumstances.
Wife Protecting Husband
- When one’s wife is with him, there is no problem of being alone with other women as well. This only applies if one's wife is in the same room with him but not if one's wife is just in the same city.
Mother, Daughter, or Sister Breaking Yichud
- Most poskim assume that this leniency of having a very close relative such as one's wife isn't yichud and protects from yichud, applies also to one's mother, daughter, and sister as well. Therefore, if a man is in a room with his wife, mother, daughter or sister, and one other woman he does not violate the yichud prohibition. Similarly, the minhag is to permit yichud for a grandchild with one's grandmother. Then even if there's another woman there it isn't yichud because of the presence of the grandmother. Sephardim are strict that there is yichud if there's another women with whom it is permitted to have yichud.
- Some poskim allow a man to be secluded with an adopted daughter as long as his wife is alive.
- A man is allowed to be secluded with his children even if they all converted and halachically aren't related.
Open to the Public
- It is permitted for a man and woman to be secluded with one another in an area that is open to the public except at nighttime. Nighttime is defined by when people aren't traveling the streets.
- A door open to the street permits yichud even with a non-Jew or someone who is suspect to immorality.
- A door open to the street only permits that room and not rooms connected to it on other floors or even other rooms on that same floor.
- Some poskim hold that yichud is only permitted in the area visible to the street but not to areas in the room that aren't visible from outside.
Neighbor with a Key
- If a person asks a neighbor to come into his house at random times that works to void yichud. At night for this option to work some say it is necessary to have two neighbors to visit and some say that it doesn't work at all at night.
- An apartment that opens to a courtyard inhabited by three people or more, or someone who would prevent yichud such as a couple, if the door is open to that courtyard that is considered like being open to the public domain. If someone knows that the neighbors aren't going to enter one's house the door actually would have to be open and not closed but unlocked according to all opinions.
Closed But Unlocked
- Some say that as long as the door is unlocked even if it is closed that area is considered open to the public, however, some say that it is only considered open if the door is actually open. Practically, some say that one can be lenient only if people in that area enter without knocking and getting permission. Some say that in cases of need one can be lenient regarding any rabbinical form of yichud.
- According to those who hold that it is permitted to have yichud in a house that's closed but unlocked some say that the same is true with a house that is locked but others who would break yichud have the keys and can enter at any time.
A Woman One Is Comfortable With
- Some poskim hold that it is forbidden to seclude oneself with a woman which one is comfortable around in an area open to the public, while others permit it.
Windows to the Street
- If there is a window that makes the room visible from the street someone who is in front of that window is considered as though it is open to the public and there's no yichud. One condition for this to be applicable is that the window needs to be low enough that people from the street can easily see into the room normally. There are some poskim who hold that if the window is high enough that a person from the street could see in while walking on his tippy toes that is also considered open to the public, while others disagree.
- There are poskim who significantly limit the applicability of this leniency so that it is almost irrelevant. They explain that if the room has a corner or a place in it which isn't visible from the street through that window then the window isn't considered open to the public since there's a concern that a person will walk away from the window into the secluded area of that room. Furthermore, some poskim say that if the room which has a window is connected to another room that isn't open to the public then again there is no leniency by having a window the public since it is easy to walk away from the window into the other room. Yet some poskim disagree with these last two conditions and hold that a window to the public permits yichud while one is visible to the public.
Acting as a Shomer
- If there is a child who is at the age that they understand what biya is and would be able to tell others if they saw something but aren't themselves at the age of biya then they can serve as a guard (shomer) for yichud. For example, a female maid left with two boys, one above the age of 9 and one that is 8 then the 8 year old is a guard (shomer) for the other child. The 9 year old would generally be forbidden in yichud with the maid, however, an 8 year old isn't obligated in yichud and is also old enough to be a shomer to prevent yichud.
- A male that is below 9 can act as a shomer once they know what the idea of biya is and could tell others if they saw something suspicious, however, once they're above 9 they can't be used as a shomer since they are forbidden with yichud themselves. Some say that from the age of 7 or 8 can be used, each one according to their knowledge. Some say that in a case of need even a child from the age of 5 or 6 can be used. Some say that even a child above 9 until they are 13 can be used as a shomer.
- Some say that it is forbidden for a man and woman to seclude themselves together even if there's a camera or webcam that makes everything in the room visible to onlookers in another location.  If someone is monitoring the camera, some poskim say that one can be lenient. 
- According to Sephardim, if on the road at that time there's on average a car every 3 minutes and it is possible to see inside the car then there's no yichud for a man and woman together in a car. If the road isn't heavily traveled it is forbidden unless there are three men and three women, such as on a bus. However, on a bus where there was three men and three women and then some of them leave, if a woman is left alone with a male driver the woman must exit the bus unless there is a danger to get off.
- According to Ashkenazim, some say that it is not proper for a man and woman to travel alone in a car, while many others say that it is only forbidden to travel alone on small streets, where there only a few cars on the road.
- It is permissible for a man to enter an elevator with a woman because the time in travel is usually very short. Some say that it is permitted if the elevator has a travel time of less than 3 minutes. 
- If the building doesn't have a lot of people on each floor such as in an office building after hours, taking the elevator with one man and one woman is an issue of yichud.
- Many authorities hold that one man may not be in the same house as a woman even if they are in different rooms. However, Sephardim hold that technically there is no yichud if they aren't in the same room. They must be vigilant to make sure that they don't come to forbidden yichud by using the shared area at the same time.
- If a woman locks herself in a room and the man in on the outside room for Ashkenazim that is considered yichud. However, for Sephardim it isn't considered yichud.
Doctor and Patient
- For a dentist/doctor, yichud may be permitted if one is caught up in his work to the point that he will not do anything inappropriate. This leniency doesn't apply if the patient is the doctor's last patient unless there is a secretary or someone else in the office who is waiting for the doctor to come out of the room. Some poskim don't hold of this leniency alone for yichud. Some poskim are lenient as long as the room is unlocked and others can enter.
- A second potential heter for yichud for a dentist/doctor is that he/she will receive professional repercussions if he/she would act inappropriately. This suffices as a preventative measure.
- A third way to avoid yichud is by ensuring that other individuals can see inside the room or by simply making sure others are present.
- If when a dentist sees a patient he/she closes the door, if others commonly walk in, it could be permitted. But if other people never walk in when the door is closed, it would be assur.
- The relationship between a dentist/patient can be transformed into a libo gas ba situation if they develop a relationship through the professional interactions. Then these heteirim would not apply.
- The minhag is to permit a man to teach children if he's married even if his wife isn't in the same city.
- A woman can be a teacher for young boys if her husband is in the town all the time (so that no issue of yichud arises).
Men secluding with other men
- Technically there is no prohibition of yichud for two men to be secluded in the same room since there is no concern that Jewish would violate the prohibition of mishkav zachur. However, it is praiseworthy to be strict to avoid seclusion of two men together.
- It is forbidden for two men to sleep in the same bed.
- Article on Selected Halachos relating to Parshas Achrei Mos by Rabbi Doniel Neustadt
- Practical Applications of Hilchos Yichud by Rabbi Uri Orlian
- Minchat Ish by Rav Ayal Sharga, the son of Rav Baruch Sharga, a major Sephardi Rosh Kollel in Eretz Yisrael. (Volume One, Volume Two), useful for Sephardim in the absence of extensive Teshuvot from Rav Ovadia
- Gan Naul, another useful Sefer for Sephardim
- Shulchan Aruch EH 22:1-2, Aruch Hashulchan EH 22:1, Kitzur Shulchan Aruch 152:1, Yalkut Yosef Hilchot Ishut EH Siman 22:1-2.
- The Gemara Kiddushin 80b and Avoda Zara 36b learns from a Pasuk that Yichud with a relative who one is forbidden to live with (someone who would be in the category of Arayot) is prohibited. The Gemara (Avoda Zara 36b) explicitly calls Yichud with a married women to be a biblical prohibition. Thus, Tur EH 22:1 writes that Yichud with an Erveh is biblical. The Rambam (Issurei Biyah 22:2), however, argues that Yichud is only Divrei Kabbalah. Bet Yosef (EH 22:1) explains that the Rambam holds that the gemara's expression that Yichud is biblical only meant that it is hinted to in the Torah, but Bet Yosef isn't clear if according to Rambam it is a biblical prohibition or rabbinic. However, Bet Shmuel 21:1 understands that Rambam holds that holds that all of yichud is only rabbinic. Otzar Haposkim 22:1:1 quotes that this is also the view of Levush, Atzei Arazim, Ayin Yitzchak, Ben Yamin, and Tuv Taam V'daat. On the other hand, Otzar Haposkim quotes Mabit, Ara derabbanan, Yair Ozen, and Chikrei Lev who argue that even Rambam holds it is a biblical prohibition.
- The Perisha EH 22 posits that there's a biblical prohibition to have yichud with someone who is forbidden on a biblical level (lav). Chazon Ish EH 34:6 agrees.
- The Gemara Avoda Zara 36b says that the Bet Din of Dovid HaMelech instituted the prohibition of Yichud with a single woman and Bet Shamai and Bet Hillel extended Yichud to a non-Jewish woman as well.
- Does the prohibition of yichud include a concern of rape or just seduction? Igrot Moshe 4:65:12 and 4:65:19 writes that yichud was instituted for seduction or mutual consent and not rape. This is also the opinion of Binat Adam (Teshuvot Shaar Bet Hanashim n. 26). He has two proofs: 1) the Gemara Kiddushin 80b says that the concern of yichud of one man and two women is that they might both agree to seduction and does not mention a concern of rape. 2) A woman whose husband is in the city may seclude with a man because she wouldn't sin because of fear of her husband (Rambam). If the concern was rape then this would be forbidden. However, he raises the question that Dovid made yichud even with unmarried women because of a story of Amnon's rape of Tamar. That implies that the concern of yichud is for rape. He answers that Dovid made the yichud for single women because if he would have instituted it earlier then even that case of Tamar's rape wouldn't have happened. However, Bach 22:7 and Bet Shmuel 22:15 hold that yichud is forbidden because of a concern of rape. That is how he explains why it is forbidden to have yichud with a girl above 3 years old even though there's no concern of seduction at that age.
- Is there a concern that if a man and woman currently aren't in a state of yichud that they will move into a state of yichud such as with a car since they might drive to a deserted alley? Igrot Moshe EH 4:65:2-3 is concerned for this. He says that this seems to be the dispute between Rabbenu Yerucham and Maharshal in Bet Shmuel 22:9 and we follow the Maharshal.
- Pitchei Teshuva 22:1 quotes Chovat Yair that yichud deoritta is limited to one man and one woman, but one man with two women is only rabbinic.
- Shulchan Aruch EH 22:6
- Birkei Yosef EH 22:3, Pitchei Teshuva 22:5, Chelkat Mechokek EH 22:6 based on the Maggid Mishna but himself questions it. Igrot Moshe 4:65:15 agrees. Bet Shmuel 22:8 writes that "many women" means 3 but he doesn't explain what "many men" means.
- Chachmat Adam 126:3 writes this and cites Bet Shmuel 22:8
- Bach 22, Taz 22:3
- Igrot Moshe EH 4:65:15
- Pitchei Teshuva 22:6 citing Birkei Yosef. This is also suggested by Chelkat Mechokek 22:9 and Bet Shmuel 22:11.
- Rama E.H. 22:5
- Igrot Moshe EH 4:65:14
- Igrot Moshe 4:65:20
- Yalkut Yosef Hilchot Ishut EH Siman 22:10. According to Yam Shel Shlomo (Kiddushin Siman 20) and Sh"t Maharsham 3:152, one man with two women is a biblical prohibition. Sh"t Chavot Yair 73 holds it is only rabbinically forbidden. See also Sh"t HaRashba 1:587.
- Rama E.H. 22:5
- Shulchan Aruch E.H. 22:5, Yalkut Yosef Hilchot Ishut EH Siman 22:10
- Yalkut Yosef Hilchot Ishut EH Siman 22:1, Gan Naul pages 9-10.
- Otzar Haposkim 22:3:3 quotes Od Yosef Chay, Tzitz Eliezer, Imrei Dovid, Ezer Mikodesh, and Aruch Hashulchan who hold that both types of granddaughters are permitted, unlike Meorot Natan based on Nodeh Beyehuda 2:18 who holds that a son's daughter is forbidden.
- Chelkat Mechokek 22:1, Yalkut Yosef Hilchot Ishut EH Siman 22:1, Gan Naul pages 9-10. Igrot Moshe EH 4:64 writes that the exact amount of time isn't critical, it is only permitted if they're only there as a guest in a very evident way and not living there for some period of time. However, Bet Shmuel 22:1 suggests that secluding with a sister is forbidden since Rambam, Tur, and Shulchan Aruch make no mention of it being permitted. Otzar Haposkim 22:4:1 quotes Od Yosef Chay, Yafeh L'lev, Yosef Ometz who are strict about this. However, they also quote Prisha, Chikrei Lev, Maharshal, Chayei Adam, Maharsham, Aruch Hashulchan, and Avnei Nezer as being lenient.
- Gan Naul pages 10-12. Igrot Moshe EH 4:64:3 explains that a sister and brother can have yichud only if he’s visiting and not living there even temporarily. If parents leave for a time and brother and sister are both staying at home, it is permitted for a short period of time. However, if both parents leave for an extended period of time like to go to Eretz Yisrael it is a problem. See Igrot Moshe EH 4:65:11 concludes that this depends on the particular situation.
- Igrot Moshe EH 4:64 at the end
- Shulchan Aruch EH 22:7, Yalkut Yosef Hilchot Ishut EH Siman 22:7
- Aruch Hashulchan EH 22:6 held that a professional acquaintance is considered libo gas ba but the Tzitz Eliezer 40:12:2 disagreed and quotes the Chida in Shaar Yosef 3 who is lenient.
- Igrot Moshe EH 4:65:6 is strict if the man has a job and can't come home in the middle of the day that it isn't considered baala b'ir even though technically he is in the same city as her. However, if he works for himself and can come home whenever he wants then the leniency of being in the city does permit her in yichud.
- Yalkut Yosef EH 22:7 is lenient even if the husband is on the other side of town or he doesn't know in where his wife currently is.
- Chachmat Adam 126:6
- Igrot Moshe 4:65:21
- Shulchan Aruch Even Haezer 22:5. Beit Shmuel 22:8 says that the reason for this leniency is that one’s wife is assumed to watch him to avoid sinning.
- Igrot Moshe EH 4:65:5
- The Pitchei Teshuva EH 22:2 does not extend this Heter to one’s daughter (meaning a man, his daughter and another woman would violate Yichud), while Iggerot Moshe (Even Haezer 2:15) extends it to a daughter and in Iggerot Moshe 4:65:8 extends it to a mother, and sister as well. He writes that these women permit him even with a non-Jewish woman since he would be embarrassed to sin in front of his daughter, mother, or sister.
- The Nitei Gavriel Yichud 40:1 follows Rav Moshe (and in footnote 1 quotes many others who do as well).
- Rav Soloveitchik as cited in Nefesh Harav p. 256 was lenient about a man with his grandmother even though there was another one of his female cousins there since the man with his grandmother isn't yichud and the grandmother protects him from yichud with another woman. Rav Schachter comments that this is in accordance with Igrot Moshe EH 2:15.
- The Chida in Yosef Ometz 26 writes that even though it is permitted to have yichud with one's mother it is certainly forbidden to have yichud with your mother and another women with whom yichud is forbidden. He explains that the only reason it is permitted to have yichud when one's wife is there is because she'll protect him from sin, whereas a mother won't. Minchat Ish 1:11:1 quotes the dispute between the Chida and Rav Chaim Palagi and is strict unless it is only derabbanan yichud. Gan Naul 12:2 is strict unless there is a situation of need in which case there is what to rely upon to be lenient. He cites that Rav Moshe Halevi and Chacham Ben Tzion Abba Shaul were strict on this issue.
- Igrot Moshe EH 4:46:2 allows yichud of a parent with an adopted child of the other gender as long as the other spouse is still alive. His reason is that one spouse will protect the other one from sinning as long as they’re alive.
- Igrot Moshe EH 4:64:1 permits a man with his daughter who converted to be secluded together since a man isn’t attracted to his daughter. Gan Naul (2:8 fnt. 22 p. 155) is also lenient.
- Kiddushin 81a, Shulchan Aruch EH 22:9
- Beer Heitev 22:9, Kitzur Shulchan Aruch 152:5. Igrot Moshe EH 4:65:5 is strict and writes that even in a big city practically there's no case that one can assume that there's a concern of someone entering all hours of the night.
- Dvar Halacha 3:14 quotes the Knesset Hagedola and others that the definition of night for public depends on when people are traveling the streets. He cites the Chazon Ish who said that in Bnei Brak he ruled until 10pm it is considered open to the public.
- Chida in Birkei Yosef 22:9 and Shaar Yosef 3. Dvar Halacha 3:17 agrees. Otzar Haposkim 22:9:11 cites this Chida and no one else on the issue.
- Knesset Hagedolah (Hagahot Tur EH 22:11) writes that a door that's open to the street only permits that room and not the upper or lower floors connected to that room. The Otzar Haposkim 22:9:5 quotes the Apei Zutrei 22:20 and Nichpeh Bkesef who agree.
- The Otzar Haposkim 22:9:5 quotes the Nidrei Zerizin 2:9 and Bet Shlomo OC 48 who write that rooms connected to a room open to the public are still subject to yichud, only the room that is open to the public itself is permitted. On the other hand, the Ezer Mkodesh seems to be lenient. Dvar Halacha 3:9 quotes this dispute and adds that the Bet Meir is strict but the Maharsham is lenient.
- Nitai Gavriel 32:5 writes that any spot in the room that isn't visible from the outside is forbidden. He supports this from the Bet Shlomo 48, Ezer Mkodesh, Yad Yitzchak 3:220, and Misgeret Hashulchan 152:10
- Gan Naul 8:11. There he quotes Dvar Halacha p. 188 who says that giving a key to a neighbor and telling him to come and he actually comes is a heter of yichud. Rav Shternbuch in Teshuvot Vehanhagot 2:657:2 agrees. Gan Naul also quotes Rav Elyashiv (Kovetz Bet Hillel). Nitai Gavriel Yichud 5:6 advises giving the key to two neighbors. Teshuvot Vehanhagot 1:774 also mentions having two neighbors visit. Om Ani Choma CM 386 agrees. Nishmat Avraham 22:3 allows if the wife has a key. Gan Naul concludes with Rav Rasavi that if the neighbor doens't actually enter one should ask another neighbor.
- Dvar Halacha 3:5
- Rashba (responsa 1:1251)
- Pitchei Teshuva 22:8 quoting the Beit Meir and Rabbi Akiva Eiger (responsa 100)
- Nitai Gavriel (Yichud 33:1), Dvar Halacha (responsa 26). See Igrot Moshe EH 4:65:4 who is lenient regarding yichud in a room with the door unlocked to the public since almost everyone would answer the door if someone knocked and he's afraid of someone entering unless it is locked. He adds that this is only applicable if generally people would enter the house without permission if it is unlocked.
- Rabbi Uri Orlian in a shiur on yutorah.org (min 70-3)
- Dvar Halacha 3:3 quoting the Chazon Ish
- The Chelkat Mechokek 22:13 writes that a person who is comfortable around a certain woman is forbidden to seclude himself with her in an area open to the public. Bet Shmuel 22:13 agrees. The Taz 22:9, however, disagrees and permits. Chida (Birkei Yosef 22:6 and Birkei Yosef 245:6) proves from Shulchan Aruch and others that it is permitted but he isn't willing to be lenient. Kitzur Shulchan Aruch 152:5 rules like the Chelkat Mechokek. Misgeret Hashulchan 152:10 cited by Otzar Haposkim 22:9:13 is lenient in extenuating circumstances. Nitai Gavriel (Yichud 32:7) writes that in cases of need such as with a doctor one may be lenient unless the person is comfortable around the woman in an inappropriate sense. Tzitz Eliezer 6:40:12:4-8 is lenient. Gan Naul 8:25 seems to be lenient. He quotes the Shevet Halevi 5:23:7 and Divrei Chachamim 5:11 as permitting, while the Nodeh Beyehuda EH 2:18, Aruch Hashulchan 22:6, and Igrot Moshe (EH 4:60 s.v. v'gam) are strict.
- The Nodeh Beyehuda 1:71 writes that a window that is visible to the public is considered like the room is open to the public and there's no yichud. Otzar Haposkim 22:9:4 quotes the Maharsham (Introduction to 2:76) who is lenient if you the window is high but can be seen from another house if someone in that other house were to stand on a chair, however, he isn't lenient with the same situation if you could only see from the street if you were to get on a chair. Gan Naul 8:18 rules like the Maharsham. Tzitz Eliezer 6:40:11:8 holds that a window permits yichud even if it is only possible to see in from the public while standing on one's tippy toes. Igrot Moshe EH 4:65:2 seems like he is only lenient with a window if you can be seen normally and not that a person needs to get on his tippy toes. However, the Gan Naul (ch. 8 fnt. 59) explains Igrot Moshe in accordance with the Maharsham.
- The Ezer Mkodesh 22:9 (cited by Otzar Haposkim 22:9:4) writes that if the room which the window is open to has a corner or secluded area which isn't visible from the window then the window doesn't permit anything since there's a concern that the man and woman will walk into that secluded area. The Bet Yitzchak Glick 3:220:2 and Misgeret Hashulchan 52:10 quote this.
- Igrot Moshe EH 4:65:2 writes that if the room in which there's a window is open to another room that isn't open to the public then yichud is prohibited even in front of the window. Gan Naul 8:16 fnt. 56 explains Igrot Moshe in this vein. See the previous footnote for the explanation.
- Gan Naul 8:16 proves from the Nodeh Beyehuda and others that there is no concern that someone who is currently not in a state of yichud will enter into a state of yichud. As such he writes that standing in front of the window that is visible to the public undoes yichud even if it is easily possible to walk into a secluded area. Gan Naul quotes Rav Elyashiv as being lenient on a window in the room even if there are secluded parts of the room as long as one is in front of the window. Dvar Halacha 3:13 agreed.
- Gan Naul ch. 1 fnt. 51, Minchat Ish by Rav Shraga Ayal 10:2. Shevet Halevi 10:237 seems to allow it in cases of need.
- Minchat Ish by Rav Shraga Ayal 10:2
- Kuntres Internet BeHalacha (p. 33) discusses whether having a webcam is similar to having a door open to the public domain and in the conclusion quotes Rav Elyashiv saying that it is not a valid leniency.
- yichud with video-camera. They also write that it is possible that it is also permissible if it is recording, even if nobody is watching. see also Rabbi Eli Mansour DailyHalacha. Rabbi Aryeh Lebowitz in a Ten Minute Halacha explained that it seems that a security camera that can be monitored at any time is enough to prevent yichud.
- Yalkut Yosef Hilchot Ishut EH Siman 22:9, Gan Naul 8:22. Gan Naul cites Rav Meir Mazuz in Or Torah 18:108:37 as agreeing.
- *Rav Moshe in Sh”t Igrot Moshe EH 4:65:3 writes that initially it is not proper for a man and woman to travel alone because of a concern that they may stop in a deserted area and do something inappropriate. However, in a case of pressing need such as if a woman in the community needs to go to the same place he’s traveling and if he refuses he’ll be considered selfish, one may rely on those who hold that there’s no concern that they will stop in a deserted area. He compares this to a discussion in the Bet Shmuel 22:9.
- However, Rav Shlomo Zalman in Minchat Shlomo 1:91(21) writes that sometimes there's room to be lenient to rely on the fact that the car has windows which are visible to the public and that there's no concern that they may stop in a deserted place. (See there for more details). Additionally, Rav Vosner in Shevet HaLevi 5:202(1) writes that regarding the nighttime concern, there's room to be lenient since the person driving can't fall asleep, however, he adds that since sometimes intercity highways or even local streets become deserted at night one should be strict.
- Lastly, Rabbi Jachter quotes Rav Mordechai Eliyahu (cited in Techumin 10:311), Rav Aharon Lichtenstein, and Rav Mordechai Willig as ruling that it is permitted for a man to travel alone in a car with a woman unless they are driving in a very remote area or at a time when there are very few cars on the road. Nitei Gavriel (Yichud 44:1) rules that one roads where cars continue to pass by and the roads are well lit, there's no Yichud, however, on small streets where not very many cars travel it's forbidden. See further Rabbi Mansour on DailyHalacha.com.
- Rabbi Jachter quoting Teshuvot Igrot Moshe E.H. 4:65:16, Teshuvot Tzitz Eliezer 6:40:22, and Rav Shlomo Zalman Auerbach (Minchat Shlomo 1:91:22) say that it is permitted for a man to enter an elevator with a woman and it isn't yichud.
- Yalkut Yosef (Chinuch pg 389), Gan Naul 8:21. Rav Orlian mentions that potentially going up the glass elevators in CN towers in Toronto which are taller than 1100 ft and the elevators take 58 seconds is a bit of a question of yichud if a man and woman go in together.
- Minchat Ish 14:5 explains that the poskim were lenient on going into an elevator in yichud because it wasn't possible to remain in yichud for a long time. However, if the floors it wouldd open to wouldn't have a lot of people, then it is yichud.
- Sh"t Igrot Moshe 4:65:19. Otzar Haposkim 22:28:5 quotes a dispute between the poskim within Rashi if locking the door between the room where the man is and where the woman is avoids yichud. Tzitz Eliezer and Divrei Malkiel hold that it is permitted even for Rashi and Ashkenazim. Rabbi Aryeh Lebowitz explains that even though Rav Moshe is strict there are some are opinions who are lenient but does not give a final ruling. See also Salmat Chaim 151, Chazon Ish 34:1-2, Shaar HaTziyun 239:27, Chachmat Adam 126:7, Divrei Malkiel 4:22, Tzitz Eliezer 6:40 (chap 7:10).
- Gan Naul 6:3. Otzar Haposkim 22:28:4 quotes this understanding of Rambam and Shulchan aruch from Chelkat Yakov and Binat Adam, but Chazon Ish wasn't sure.
- Igrot Moshe EH 4:65:19
- Gan Naul 6:3
- Igrot Moshe (E”H 4:65:1) says that a male OBGYN is so caught up in his work that he will not have any illicit desires. He continues that even after he completed seeing the patient and other patients are waiting and he is not necessarily busy with the work at this moment, he doesn’t have time to linger around and must rush to the next patient, so there is no potential issur that he will do in that short time span. If it is the end of the day and no more patients are coming, he can rely on the secretary or someone else in the building to mitigate the issur yichud.
- Rav Shlomo Zalman Auerbach quoted in Nishmat Avraham (v. 3 22:1:3 p. 203) quotes the Gemara Kiddushin 80b which says that yichud applies even to a man and woman who are burying a baby in a cemetery, showing that there is an issur yichud even when one is busy with something where theoretically there should be no yetzer hara.
- Shevet Halevi 5:203:6, Nishmat Avraham v. 3 p. 203 quoting Tzitz Eliezer 6:40:12:10-12
- The Otzar Haposkim 22:8:7 quotes the Yaskil Avdi 2:17, Tzitz Eliezer 6:40:12:8. Nishmat Avraham as quoted by Rabbi Mordechai Torczyner. Tzitz Eliezer says that this heter may potentially only apply when both individuals involved are busy with the work. In a dentist/patient relationship, only the dentist is preoccupied, so the heter may not apply. See Chazon Ish EH 35:2 regarding this approach.
- Igros Moshe E”H 4:65:2 says that if a window is low enough for people outside to see, there is no yichud. But if the window is very high to the point that the people outside must climb up a ladder to see inside, which is very unnatural, that would be an issur yichud. When it comes to a dentist/patient, if they are visible to the public through a window, that can potentially avoid yichud.
- Rav Moshe Shternbuch says that if one goes to a dentist/doctor of the opposite gender, one should bring his/her spouse or another relative.
- Rav Shlomo Zalman Auerbach
- Rav Shlomo Zalman Auerbach, quoted in Nishmat Avraham 3:94-95
- Igrot Moshe EH 4:65:13 writes that the minhag is to follow Rabbi Akiva Eiger who is lenient on this. This is unlike Chelkat Mechokek 22:21 who writes that a man may not teach children unless his wife is in the town, otherwise there is a concern that he will become close to the mothers who drop off and pick up their children and sin with them.
- Igrot Moshe EH 4:65:18. Igrot Moshe rules like Chelkat Mechokek unlike Taz who requires that her husband is in the same house.
- Shulchan Aruch E.H. 24:1
- Chelkat Mechokek 24:1, Bet Shmuel 24:1